Poppet-type valve assemblies are well known. Such a valve assembly typically includes a valve body having a seated port and a pintle having a valve head for closeably mating with the seat. The pintle is axially reciprocable through a bore formed coaxially with the seat in a wall of the valve body opposite the seat. The bore may be provided with a press-fit sleeve bushing for the pintle, the bushing being formed from a durable, low-friction material different from the material of the valve body and the pintle. Press-fitting the bushing serves two purposes: to seal against leakage around the bushing and to center the pintle in the bore.
Press-fitting requires very tight manufacturing tolerances in the valve bore, the seat, and the bushing, which results in high manufacturing cost, difficult quality control, and complexity. In addition, a tight press-fit can generate large assembly forces which can distort the components and misalign the seat and bore, causing increased manufacturing waste or later leakage and premature failure.
In some applications, poppet valves are exposed to a wide range of temperatures during operation. One such application is as an exhaust gas recirculation (EGR) valve for an internal combustion engine, wherein operating temperatures may range between, for example, −40° C. and 750° C. Because the valve body and bushing are formed of different materials, thermal stresses may add to the assembly stresses which can result in thermal fatigue and/or render the bushing free in the bore, either of which results in failure of the EGR valve.
What is needed is a means for relieving the tolerance requirements of a valve body bore and valve bushing while maintaining sealing of the bushing to the body and centering of the bushing in the bore.
It is a principal object of the present invention to relieve the tolerance requirements of a valve body bore and valve bushing while maintaining sealing of the bushing to the body and centering of the bushing in the bore.
It is a further object of the invention to provide such relief and centering over the range of operating temperatures experienced by the valve.
It is a still further object of the invention to reduce the cost and complexity of manufacture of a poppet valve assembly.